1. Field of the Invention
The present invention relates to an image decoding apparatus, capable of simultaneously outputting images with different image formats, a semiconductor device, and an image decoding method.
2. Background Art
Recently, two moving image coding standards called MPEG (Moving Picture Expert Group) have been practically used as the moving image coding systems; one is MPEG 1 (International Electric Communication union ITU-T Recommendation H. 261), which is a standard for moving image and storage media and the other is MPEG 2 (ITU-T Recommendation H. 262), which corresponds to a standard for higher image quality and high speed coding. Among these standards, the MPEG 2 has been widely noticed as a media integrated moving image coding standard in joint operations of the fields of communication, accumulation, broadcasting, and computer. MPEG 2 provides the image quality of present television system such as the present NTSC system with an information amount of 4 to 9 megabits, and provides the image quality of HDTV (high resolution television) with an amount of information of 15 to 30 megabits. An explanation is provided below of MPEG 1 and MPEG 2 referred to as a whole as MPEG.
FIG. 6 is a block diagram showing the structure of the conventional image decoding apparatus, wherein the input coded data correspond to coded bit stream in the form of the above MPEG. As shown in FIG. 6, the conventional image decoding apparatus comprises a coded data decoding portion 31 and an external memory portion 12.
In the above-mentioned coded data decoding portion 31, reference numeral 1 denotes an MPEG decoding portion for storing the decoded data temporarily, corresponding to the image data obtained by decoding the coded data in an external memory portion 12, and reference numeral 2 denotes a decoded data reading portion for outputting as the decoded data signal B1 after reading the decoded data from the external memory portion B1 based on the image output sequence in response to the decoded data request signal R1. Reference numeral 3 denotes an image format converting portion for generating and outputting the image after converting input decoded data signals B1 to a prescribed image format, and reference numeral 4 denotes an image synchronizing signal generating portion for generating and outputting a horizontal image synchronizing signal (not shown in FIG. 6) and vertical image synchronizing signal A1, which corresponds to the image format to be converted by the image format converting portion 3.
The above-described conventional image decoding apparatus generates an image data by decoding coded data input from the MPEG decoding portion 1 and outputs the image after converting the image data into the image data of a prescribed image format by the image format converting portion 3. The image format converting portion 3 synchronizes the horizontal image synchronizing signals generated by the image synchronizing signal generating portion 4 and the image output to the vertical image synchronizing signal A.
However, the above-described conventional image decoding apparatus is not capable of decoding input coded data and simultaneously outputting images prepared by various image formats.